Meiosis and Chromosomal Mixing (SCIENCE PDF)

# The Meiosis and Chromosomal Mixing ### Start of Meiosis - Interphase (G1) - **Prophase I:** Chromosomes condense. - **Metaphase I:** The homologous pairs of chromosomes align along the equator of the cell. - **Crossing Over (Intra-chromosomal mixing):** occurs in prophase I. Chromosomes sw...

# The Meiosis and Chromosomal Mixing ### Start of Meiosis - Interphase (G1) - **Prophase I:** Chromosomes condense. - **Metaphase I:** The homologous pairs of chromosomes align along the equator of the cell. - **Crossing Over (Intra-chromosomal mixing):** occurs in prophase I. Chromosomes swap genetic material. - **Inter-chromosomal mixing:** happens in Metaphase I. Homologous chromosomes separate. - **Cyte I (2n=4)** - **Cyte 2 (n=2)** ### Meiosis and Chromosomal Mixing - Meiosis is a type of cell division that reduces the number of chromosomes in a cell by half. - Generates genetically different cells - **Inter-chromosomal mixing:** Pairs of homologous chromosomes separate during Meiosis, and this separation occurs randomly. - **Intra-chromosomal mixing:** Crossing over occurs during prophase I, resulting in exchange of genetic material between pairs of homologous chromosomes. - It creates genetic diversity, as new combinations of alleles are created - The number of possible genetic combinations increases exponentially as the number of chromosomes per cell increases. - 2n=4, then 4 possible combinations - 2n=6, then 8 possible combinations - 2n=46, then 8.4x10^6 possible combinations - The diversity of offspring is determined by the number of possible combinations of chromosomes. ### Genetics: Monohybridism - **Line/Race:** A group of individuals of the same species that produce offspring with similar traits. - **Diploid:** Individuals with two sets of chromosomes (2n). - **Homologous chromosomes:** One chromosome from each parent. - **Genes:** Segments of DNA that determine the structure and function of organisms. - **Allele:** One of two or more possible forms of a gene. - **Homozygous:** When both alleles for a gene are identical (AA, BB). - **Heterozygous:** When alleles for a gene are different (Aa, Bb). #### Crossbreeding chickens: - **Cross 1:** Black chicken (NN) x Black chicken (NN) - F1: 100% Black (NN) - Both parents have the same phenotpye and the same genotype so all the offspring will have the same phenotype and genotype. - **Cross 2:** White chicken (BB) x White chicken (BB) - F1: 100% White (BB) - Both parents have the same phenotpye and the same genotype so all the offspring will have the same phenotype and genotype. - **Cross 3:** Black chicken (NN) x White chicken (BB) - F1: 100% Grey (NB) - The parents have different phenotypes and genotypes, but the offspring all have the same phenotype (grey), but a different genotype (NB). - **Cross 4:** Grey chicken (NB) x Grey chicken (NB) - F2: 1 Black (NN), 2 Grey (NB), 1 White (BB) - Parents have the same phenotype and genotype, but their offspring showcase the original phenotypes and genotypes of their parents. #### Codominance: - The hybrid offspring exhibits traits from both parents. - Each allele expresses itself independently, leading to a new phenotype. ### Transmission of Alleles Linked to Sex - **Drosophila:** Fruit fly, often used for genetics research. - **Wild type:** The common or standard phenotype, in this case is red colored eyes. - **Mutations:** A change in the DNA sequence, resulting in a different phenotype, in this case, white colored eyes. #### Experiment 1: - **Parents:** Red-white (S) x Red-eyed (S) - **Offspring:** 100% Red-eyed (S) #### Experiment 2: - **Parents:** White-eyed (W) x Red-eyed (S) - **Offspring:** 50% White-eyed (W) and 50% Red-eyed (S) #### Interpretation of the Results - **Sex-linked inheritance:** The gene responsible for eye color is located on the X chromosome. - **Female:** XX, each female carries two copies of the gene - **Male:** XY, they only carry one copy of the gene - **Result:** The female flies are heterozygous for the eye color trait. 50% of their offspring inherit the W allele and are white-eyed, and 50% inherit the S allele and are red-eyed. - **Conclusion:** The sex chromosomes play a direct role in the inheritance of certain traits; the allele linked to sex can be passed down differently to the male or female offspring.